It is known that cement furnaces are large in both length and diameter and that this causes problems at the level of the furnace supports and the driving device since the furnace must be able to permanently rotate about its longitudinal axis.
The weight of the furnace, which comprises the outer metal casing, the inner refractory lining and the material being processed, is such that a bending strain of the oven is observed between the support points and even beyond. To limit the bending strain to acceptable levels, it is necessary to provide a sufficient number of supports. Dry process furnaces using preheaters are generally provided with three supports.
In addition to these permanent dynamic deformations provided for under normal operating conditions accidental events, such as local overheating or prolonged idle times, can sometimes cause exceptional deformations that are more significant in nature.
In the case of furnaces provided with three supports, these exceptional deformations can be such that when in rotation, the furnace only rests on two of the three supports, thus creating, firstly dangerous overloading in view of the mechanical strength of the supports and secondly, variations in the span (or contact surfaces) between the teeth of traditional gear drive mechanisms, a part of which is integral with the furnace while the other is fixed: this is also dangerous in terms of the mechanical performance of the systems.
With the evolution of firing processes using pre-calcinators, it has become possible to reduce the length of rotary furnaces and consider the use of only two supports: this solution has the advantage of reducing the number of mechanical parts but also of limiting the risks of a support being overloaded in the case of exceptional deformation of the furnace.
With furnaces using two supports, the problem of overloading the supports in the case of exceptional deformation is avoided but the span of the supports between the fixed roller supports and the runner surfaces which are subjected to the deformations of the furnace is no longer appropriately guaranteed due to lack of parallelism.
With furnaces using two supports, problems due to variations in the span between the teeth of traditional gear drive mechanisms are as critical as with furnaces using three supports, in the case of exceptional deformations.
To compensate for these problems it was considered, for furnaces using two supports (EP-A-0570696), to create articulated supports such that roller bearings having both driving and supporting functions could respond to deformations of the furnace. However, such a facility is complex to implement and maintain.